
//以常数的时间复杂度获取栈中的最小值

import java.util.Stack;

class MinStack {

    Stack<Integer> stack;
    Stack<Integer> minStack;

    public MinStack() {
        stack=new Stack<>();
        minStack=new Stack<>();
    }
    
    public void push(int val) {
        stack.push(val);
        if(minStack.empty()) {
            minStack.push(val);
        }else {
            Integer peekVal=minStack.peek();
            if(val<=peekVal) {
                minStack.push(val);
            }
        }
    }
    
    public void pop() {
        if(stack.empty())return;
        int popVal=stack.pop();
        if(popVal==minStack.peek()) {
            minStack.pop();
        }
    }
    
    public int top() {
        if(stack.empty())return -1;
        return stack.peek();
    }
    
    public int getMin() {
        if(minStack.empty())return -1;
        return minStack.peek();
    }
}
